MODFLOW - Optional Packages, Pt 1

[@mehakmanzoor1768]

Sir you explain everything in detail, Looking forward to learn more about Modelling through your lectures. Tysm

[@normjones]

Thank you!

[@julianaalbano7937]

great explanation. Thank you!

[@jonasj8725]

Hey, may I ask a late question? If I want to model the actual width of the river correctly, do I implement an arc as usual and assign river package parameters (including width) to it? Because the river's surface area in my case is broader than one cell and it is important to have this in the model as I have wells left and right and want to have the right hydraulic gradient calculated. The alternative idea would be to draw two arc with river package for left and right river bank, respectively. Thank you in advance if anybody reads this :D

[@normjones]

Hey, that sounds like an interesting problem. Typically we use arcs to simulate rivers and the conductance per unit length value that you assign to the arc includes the width of the river as part of the conductance, but it is a single value for the entire arc (average width over the river reach). So even though the river object is assigned only to the cells overlapped by the arc, the full width would be implicitly represented. However, there could be exchange of water between the other cells overlapped by the river. Another option you could consider is to use the General Head package and represent the river as a polygon. This would ensure that all cells overlapped by the river are properly linked to the river. Keep in mind that with the general head package there is always a direct hydraulic connection between the river and aquifer and Q is proportional to the head difference. With the River package, the river becomes disconnected once the head is below the river bottom elevation and Q becomes limited. But if you have a large river, there is probably a strong hydraulic connection anyway. Also, another challenge with using a general head polygon is assigning the river stage is a spatially varying manner. With a river arc, the stage is linearly interpolated along the length of the river. With general head we often use a single value, but there is an option in the Attribute table dialog to assign the general head stage to a TIN or Raster of river stage elevations. By the way, as I typed this up, I just launched GMS and checked and it appears that you can associate the River package with polygons in the map module as well as general head. So it would work either way. Again, you would need to set up a TIN or raster to define your river stage and river bottom elevation, but that could certainly be done. Good luck!